Conventionally, an ultrasonic sensor has been proposed that includes a piezoelectric element joined to an acoustic matching layer made of resin or the like. In such an ultrasonic sensor, an ultrasonic transmitter emits an ultrasonic wave, the emitted ultrasonic wave is reflected from an object to be detected, and an ultrasonic detector receives the reflected ultrasonic wave. Based on the received ultrasonic wave, the ultrasonic sensor can detect a distance from the object.
When an ultrasonic sensor includes multiple ultrasonic detectors that are arranged in an array, a location and a shape of the object can be detected based on time and phase differences between ultrasonic waves received by the respective ultrasonic detectors.
For example, in an ultrasonic sensor disclosed in JP-A-2006-234523, multiple ultrasonic detectors are arranged in a grid pattern. For another example, in an ultrasonic sensor disclosed in JP-A-S54-61590, a piezoelectric body bonded to an acoustic matching layer is sectioned by a slit into multiple parts that are arranged in an array.
In the ultrasonic sensor disclosed in JP-A-2006-234523, a large number of man-hours are required to arrange the ultrasonic detectors in the grid pattern. Further, it is difficult to cause the ultrasonic detectors to be accurately positioned with respect to each other. In the ultrasonic sensor disclosed in JP-A-S54-61590, although the piezoelectric body is sectioned into multiple parts, the acoustic matching layer is not sectioned. Therefore, an ultrasonic wave propagating through the acoustic matching layer cannot be separated. As a result, noise occurs, and vibration of the ultrasonic wave is damped (i.e., weakened). The noise and the vibration damping may result in a reduction in a detection sensitivity of the ultrasonic sensor.